The conspiracy trial of three former top FBI officials was postponed indefinitely yesterday after a government prosecutor told a federal judge that he needs more time to determine whether to turn over highly classified documents for use by defense lawyers.

U.S. District Court Judge William B. Bryant ordered the prosecutor, special assistant U.S. attorney Barnet D. Skolnik, to give him a report March 15 on what progress he is making in deciding what to do about the case, which now has been delayed several times.

The trial of L. Patrick Gray III, former acting director of the FBI, W. Mark Felt, the FBI's former number two man, and Edward S. Miller, former head of the FBI's intelligence division, was scheduled to start Monday. They are charged with conspiring to violate the civil rights of friends and relatives of the terrorist Weather Underground in the early 1970s by approving allegedly illegal breakins of their homes.

The latest delay results from Bryant's secret rulins last week requiring the government to turn over the classified documents to defense attorneys. The documents, which could become public at the trial, include some from the Central Intelligence Agency, the super-secret National Security Agency and foreign governments.

In part, Felt and Miller are claiming that they approved the breakins on Gray's authority, but they also say the breakins may have been legal because of alleged Weather Underground contact with hostile governments, such as Cuba and North Vietnam. Gray is claiming that he did not authorize the breakins.

Skolnik told Bryant that the prosecutors "intent to explore all kinds of options" to give the defendants a fair trial. He also said that Gray likely will have to be tried separately from Felt and Miller, but that the government has not fully decided whether that is necessary.